The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The disclosure is related in general to wellsite equipment such as oilfield surface equipment, oilfield cables and the like.
As oil and gas exploration evolves, wells are drilled to increasing depths and in increasingly harsh conditions. Cables used in the oilfield industry can be subjected to repeated physical stress, high temperatures, hydrocarbon solvents, and high concentrations of hydrogen sulfide (H2S). Greater demands are being placed on electrical conductors to carry electricity to these increasing depths.
When polymer insulated or jacketed metallic members are run into and out of an oil well, there are mechanical forces acting at the interfaces between metals and polymers. There may be separation of polymer from the metallic interfaces due to the deformation of polymer when such components are bent, when the cable passes over sheaves or rollers, when the cable passes through a stuffing box or packers that are used for pressure control, when there is a coefficient of thermal expansion difference between polymer and metal, when there is gas migration between polymer and metal interface, and when any similar operations are performed. These physical stresses may cause the polymeric covering to pull away from the metal and leave air gaps. In the case of electrical conductors, these air gaps may lead to the development of coronas.
As shown in FIGS. 1A to 1B, a standard cable 2 having at least one metallic strand 4 and a non-bonded polymer insulation 6 may have small air gaps 7, even when initially manufactured. In particular, when the standard metallic cable 2 is subjected to repeated bending, for example, when passing over sheaves (not shown) or the like, the polymer insulation 6 may pull away from the at least one metallic strand 4 and create or increase a size of the air gaps 7. The air gaps 7 in turn may undesirably create coronas in the standard cable 2. The air gaps 7 may also undesirably create a pathway to allow downhole gases (such as corrosive Hydrogen sulfide or H2S) to travel along the standard cable 2.
The presence of H2S in well fluids may result in failures when standard galvanized improved plow steel (GIPS) armor wires are used as strength members. H2S in the form of a gas or a gas dissolved in liquids may attack metals by combining with them to form metallic sulfides and atomic hydrogen. The destructive process is principally hydrogen embrittlement, accompanied by chemical attack. Chemical attack is commonly referred to as sulfide stress cracking. H2S attacks metals with a wide variation in intensity. Many commonly used carbon and alloy steels are susceptible to H2S damage. High-strength steels used in armor wires, which may have high carbon content and may be highly cold-worked, may be particularly susceptible to H2S damage.
Some metals and special alloys such as, for example, the nickel-steel alloy HC265, are very resistant to H2S attack. However, these special alloys may have much lower electrical conductivity than standard GIPS armor wire. This is a drawback in wireline operations, where armor wire is typically used as an electrical return path.
It remains desirable to provide improvements in wireline cables and/or downhole assemblies.